NA-DIRECTED ALKYLATING-AGENTS .6. SYNTHESIS AND ANTITUMOR-ACTIVITY OFDNA MINOR GROOVE-TARGETED ANILINE MUSTARD ANALOGS OF PIBENZIMOL (HOECHST-33258)

A series of nitrogen mustard analogues of the DNA minor groove binding fluorophore pibenzimol (Hoechst 33258) have been synthesized and eval uated for antitumor activity. Conventional construction of the bisbenz imidazole ring system from the piperazinyl terminus, via two consecuti ve Pinner-type reactions, gave low yields of products contaminated wit h the 2-methyl analogue which proved difficult to separate. An alterna tive synthesis was developed, involving construction of the bisbenzimi dazole from the mustard terminus, via Cu2+-promoted oxidative coupling of the mustard aldehydes with 3,4-diaminobenzonitrile to form the mon obenzimidazoles, followed by a Pinner-type reaction and condensation w ith 4-(1-methyl-4-piperazinyl)-o-phenylenediamine. This process gives higher yields and pure products. The mustard analogues showed high hyp ersensitivity factors (IC50 AA8/IC50 UV4), typical of DNA alkylating a gents. There was a large increase in cytotoxicity (85-fold) across the homologous series which cannot be explained entirely by changes in mu stard reactivity and may be related to altering orientation of the mus tard with respect to the DNA resulting in different patterns of alkyla tion. Pibenzimol itself (which has been evaluated clinically as an ant icancer drug) was inactive against P388 in vivo using a single-dose pr otocol, but the short-chain mustard homologues were highly effective, eliciting a proportion of long-term survivors.